Control for free-piston units



'Jan. 4, 1949. K. c. COOPER A CONTROL FOR FREE-PISTO N UNITS Filed April 15, 1944 INVENTORY M .4, ATTORNEY Patented Jan. .4, 1949 CONTROL FOR FREE-PISTON UNITS Kenneth C. Cooper, Portland, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application April 15, 1944, Serial No. 531,301 3 Claims. (Cl. 230-56) This invention relates to a free-piston unit adapted for operation at varying intake pressures. I

A free-piston engine-and-compressor unit designed for compressing one density of gas is improperly dimensioned for compressing gas at other densities. A feature of this invention is a unit that will operate properly at varying gas densities.

The change in density may affect the length of piston stroke and may shorten it so that the scavenge and exhaust ports in the engine cylinder will not be completely uncovered. A feature of the invention is a unit in which the eifective volume of the compressor may be adjusted to compensate for varying densities of gas.

These units may be used in aircraft power plants. The compressor, which pumps in air at the surrounding pressure if designed for high altitudes, will not be properly dimensioned for other altitudes. Another feature of the invention is a provision for controlling the volume of air compressed on each stroke of the engine to compensate for changes in altitude or gas density.

Another feature is the control of the effective volume of the compressor, by which to compensate for altitude changes, without seriously affecting the length of the piston stroke.

A feature of the invention is a number of axially spaced vents, each of which may comprise a circumferential row of openings in the compressor cylinder. The vents may be individually opened or closed to vary the volume of air compressed on each piston stroke.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings, which illustrate an embodiment of the invention.

The single figure is a sectional view through a free-piston unit.

The unit shown includes an engine cylinder i having reciprocating pistons I2 and It to which compressor pistons l6 and [8 in cylinders 20 and 22 are integrally connected. Sleeves 24 and 25 attached to the compressor pistons complete the reciprocating piston assemblies. The sleeves in combination with stationary pistons 28 and 30 form air spring cylinders.

The piston assemblies are moved apart by the burning of fuel injected into engine cylinder In through one or more nozzles 32. Air compressed.

in the air spring cylinders on the power stroke returns the piston assemblies. The assemblies are always maintained at equal distances from the 2 center of the engine cylinder by a linkage, not shown.

Intake manifold 42 which extends around the compressor and engine cylinders, conducts air to intake valves 44 in the heads of the compressor cylinders through which air alternately enters opposite ends of the cylinders. .The compressed air leaves the cylinders through discharge valves 46, also at opposite ends of the compressor cylinders, and passes into a central scavenge chamber 48 and end chambers 50 and 52. These chambers may be interconnected by a scavenge manifold, not shown.

Compressed gas from the scavenge chambers enters engine ports 54 and 56 which are uncovered by pistons l2 and it at the end of the power stroke, thereby permitting air to be blown through the engine cylinder. Gas in the engine cylinders is discharged through exhaust ports 58 into exhaust manifold 60. i

For the purpose of maintaining a substantially constant stroke, the amount of work done by the compressor on each stroke is controlled by adjusting the effective volume of the compressor. To this end, each compressor cylinder has a number of axially spaced vents 62, each in the form of a row of spill ports in the cylinders to permit air to discharge from the cylinder without compression. Each vent maybe individually controlled by a poppet valve 64, the stem 66 of which may be guided in manifold 42. Any well-known structure may control these valves; for example. as shown, the valve stem 66 may have a piston 68 sliding in a cylinder I0. A spring 12 acts on the piston to open the valve, and fluid under pressure through a conduit 14 may be admitted to the cylinder to close the valves. All the valves of any one row may be controlled by springs of the same strength so that all the valves in one row will open or close simultaneously.

The intake manifold includes a housing 82 which may extend around the compressor cylinders, and end caps 83 and 84 on the housing.

forming passages to the intake valves at the outer ends of the compressors. The vents 62 open into the intake manifold.

When the air being pumped by the compressor has a high density, as at sea level atmosphere, all the rows of ports are open and only a small volume of air is compressed. As the density decreases, as when the compressor operates at altitude, one or more of the rows of ports may be closed, beginmng with the end rows, thus increasing the eifective volume of the compressor. The several rows of ports permit adaptation of the 3 compressor to substantially any altitude or to any density of air being pumped. In this way substantially the same mass of air may be pumped on each stroke of the compressor, and by maintaining the same mass flow, the compressor does substantially the same amount of work and the stroke remains substantially constant, assuring the uncovering of scavenge and exhaust ports on each stroke.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. A free-piston engine and compressor unit including an engine cylinder and piston, said cylinder having scavenge ports therein adapted to be uncovered by the piston on each stroke for the admission of air to the cylinder, a compressor cylinder and piston, said compressor cylinder having inlet and discharge valves, said pistons being connected together and having a variable length stroke, the length of stroke being a function of the pressures in said cylinders and the work done in the compressor cylinder, and means for maintaining a length of stroke such that the engine piston will move far enough to uncover the scavenge ports on each stroke, said means including a number of vents axially spaced from each other in the wall of the compressor cylinder, each vent including a number of radially extending openings extending through the cylinder wall and arranged circumferentially. of the cylinder and means for closing all of the openings for each vent simultaneously thereby providing for adjustment of the work done on each stroke in the event of pressure changes in the compressor intake pressure.

'2. A free-piston engine-and-compressor unit 40 including an engine cylinder and piston, a compressor cylinder and piston, said cylinder having inlet and discharge valves, said pistons being connected together and having a variable lengtharound the cylinder and means for controlling all oi the openings of each vent simultaneously. 3. A free-piston engine-and-compressor unit including an engine cylinder. opposed pistons in said cylinder, compressor pistons moving with said engine pistons and compressor cylinder for the compressor pistons, said compressor cylinder having inlet and discharge valves for the fluid being pumped, in combination with means for adJusting the efi'ective volume of each compressor cylinder independently of the lengthot piston stroke, said means including axially spaced vents in the compressor cylinders, each vent including a number of radial openings arranged clrcum. ferentially of the cylinder, and means for closing all the openings of each vent simultaneously.

KENNETH C. COOPER.

REFERENCES- CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

